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Sunday, March 19, 2017

Do low levels of cardiovascular fitness predispose to cardiac hypertrophy?

There is evidence that suggests low levels of cardiac fitness predispose to maladaptive cardiac remodeling typically manifest as concentric remodeling and concentric hypertrophy and increased ventricular stiffness and diastolic dysfunction.

Lovic and Kokkinos and co workers correctly point out that the cardiac hypertrophy consequent to high blood pressure differs from the typical physiological cardiac hypertrophy of the endurance athlete realizing that extreme examples of the latter can be difficult to distinguish from the former.

Lovic et al makes the following argument in a 2016 issue of the Journal of Hypertension.

Low fitness level individuals will reach a systolic blood pressure of 150 at low levels of exercise, e.g. 4-5 METS , which are levels commonly encountered in some activities of everyday living.
150 systolic blood pressure is necessary to trigger cardiac remodeling. Individuals, who are more fit, are able to do that level of work without that degree of BP rise. So individuals with low fitness may spend considerable time each day with a BP of sufficient magnitude to trigger hypertrophic changes in the left ventricle, even though their BP as measured in their doctor's office may be normal.

Their data (1) found an inverse relationship between exercise capacity, blood pressure response to exercise and left ventricular mass.Further, they have published data that showed 16 weeks of aerobic training resulted in subjects having a significantly lower blood pressure level when they exercised at the every day activity level of 3-5 METS. A reduction in previously elevated left ventricular mass was also shown.

Other data consistent with this notion comes from a study by Brinker et al ( 2) from Southwestern Medical School in Dallas. They studied subjects aged 42 -67 years of age with stress testing and echocardiography. Those individuals in the lowest fitness category ( they divided the group into 3 fitness levels ) had 40 % concentric hypertrophy as well as a 9% prevalence of diastolic dysfunction ( as defined by the e/a ratio on mitral valve echo flow studies)

Data from the Dallas group and others have outlined the concept of there being two distinct cardiac phenotypes related to the development of both heart failure with reduced ejection fraction (HFrEF) and heart failure with preserved ejection fraction (HFpEF).They are:

Increasing data strongly suggest that low fitness levels predispose to the precursors of HFpEF.
Lovic's work suggesting that exercise induced elevated blood pressure in the unfit during the usual daily activities may be one possible mechanism involved.